Some blowout preventers of the prior art have been manually operated by handwheels and then when it is desired to convert them from manual operation to power operation, a substantially complete disassembly of the structure has been required. In such structure the threaded operation stem and cap are replaced by a piston and cylinder arrangement. A typical example of such structure is shown on page 802 of the Bowen Tools, Inc., 1976-1977 General Catalog as published by World Oil in Vol. 1. of the 1976-77 Composite Catalog of Oil Field Equipment and Services.
Also in the prior art, many blowout preventers have been hydraulically operated and have included a manual override such as shown in U.S. Pat. No. 3,692,316.
The conversion of the manual blowout preventers of the prior art has had the disadvantages of being complicated and not being able to perform the conversion while the blowout preventer is under pressure. The hydraulically operated blowout preventer with a manual override is not applicable to relatively quick in place conversion from manual operated without power to a power operated blowout preventer since it is not solely a manual operated structure.